Use of a buried flexible pipeline

Abstract

The use of a buried or covered flexible seabed pipeline for transporting fluids is disclosed. The pipeline comprises a sealing barrier (3) and reinforcing layers (4, 5) capable of withstanding mechanical stress and arranged around said sealing barrier. The reinforcing layers consist of at least two crosswise-arranged reinforcing plies (4, 5) of wires helically wound at respective winding angles a i to the longitudinal axis of the pipeline, such that they comply with the following relationships: when i=1, 2, . . . , 52°≦a i ≦58°. The arithmetic mean a m of said winding angles a i complies with the following relationship: 53°≦a m ≦57°.

What is claimed is: 
     
       1. A method of forming and installing a fluid transporting, flexible pipeline, at a seabed floor without the pipeline subsequently buckling through use, the method comprising: forming a flexible pipeline by applying reinforcing layers around a tubular sealing barrier, the applied reinforcing layers comprising at least two crossed plies of wires and the applying comprising helically winding the reinforcing layers at respective winding angles a i  with respect to the longitudinal direction of the pipeline wherein the winding angles a i  are all close to an equilibrium angle, the respective winding angles a i  of the individual wires i=1, 2 . . . being in the range of 52°≦a i  ≦58° and the arithmetic mean value a m  of the winding angles a i  of all of the wires being in the range of 53° to 57°;   the forming further comprising not applying a pressure arch to the pipeline; and   selectively placing the flexible pipeline with the applied reinforcing layers and without a pressure arch in the depth range between being on the seabed floor without material on the pipeline to a depth beneath material at the seabed floor, the depth beneath material on the seabed floor being short enough that the material at the seabed floor would not supply enough force to prevent buckling of the flexible pipeline as it is pressurized in use.   
     
     
       2. The method of claim 1, wherein the winding angles a i  =1, 2 . . . , satisfy the relationship for 54°≦a i  ≦56°. 
     
     
       3. The method of claim 2, wherein the arithmetic mean a m  of the winding angles a i  satisfies the relationship 54°≦a m  ≦56°. 
     
     
       4. The method of claim 1, wherein the winding angles a i  are approximately 55°. 
     
     
       5. The method of claim 1, wherein the pipeline further comprises tubular internal carcass inside the sealing barrier. 
     
     
       6. The method of claim 1, further comprising providing one of the reinforcing plies adjacent to the sealing barrier in the form of a winding of clipped profiled wires. 
     
     
       7. The method of claim 1, further comprising: forming a trench for the pipeline in the seabed floor, and   the placing of the pipeline comprises placing the pipeline in the trench, and applying cover of the material over the pipeline in the trench to a depth of cover of at most 0.5 m.   
     
     
       8. The method of claim 1, further comprising the placing of the pipeline comprises placing the pipeline on the seabed floor and then covering the pipeline on the seabed floor with a the material at the seabed floor to a depth of cover at most 0.5 m.